I have Windows 7 (I tried a lot in the past for the free upgrade to 10, but the computer will only perpetually restart without updating, so I gave that up).

I have an SSD, a Hard Drive, and a disk drive. My OS is downloaded on my SSD.

For some time, my Hard Drive, holding all my games, crashed here and there. It would disappear from My Computer, leaving only the SSD and disk drive active.

Since the Hard Drive crashed for good now, I made some space on my SSD for my video games and decided to live without a Hard Drive. I deleted some folders with rubbish in them, but when I restart my computer now, I get the Splash screen, followed by a "Reboot and select proper boot device or insert boot media in selected boot device and press a key" message. I'm scared I may have deleted an important folder by mistake in the SSD when I was making room. I can't remember.

I made sure the SSD is priority #1 for booting up, followed by the disc drive, which are my only two options. They don't work in any variation and I cannot get past the error message wanting me to select a proper boot device.

I lost my Windows 7 CD and key, and have trouble understanding what I need to do right now to fix this problem.

I tried plugging the SSD into another computer to see if there's any "repair windows" option or something tucked in a windows folder, but the cord won't fit to the motherboard.

Titan

You could have a friend make you a win7 install disk or flash drive to boot from to try and repair your windows.

Boot from the install disk/flashdrive as if you were going to install windows. Win7 setup will load, go ahead and enter the Language, Date/Time, & Keyboard and on the next screen instead of clicking Install Now, look below that and click on Repair your computer.

I managed to fix it! Using some softwarecalled Lazesoft, I could find out my Windows 7 CD Key, thereby letting me download an ISO, burn it or whatever onto a USB and repair windows after booting via the USB.